[Jacob-list] question on horns

[Linda]

Ahhh ..  well, thanks.  It's really clear now.. well, not exactly.  My head is genetically dense.

What confuses me is that I know it is entirely possible for a four horned ewe to have strong, 'true horn' uppers and weak, loosely attached 'scurs' as laterals.  That ewe is phenotypically horned and scurred. I believe the term "scurred ewe" as used by JSBA refers to a ewe that has nothing but scurs, rather than a ewe with only lateral scurs, so maybe I should say phenotypically 'horned, with scurs.'  Since the scur genes and the horned genes are on different chromosomes, I assume it would be possible for a sheep to be homozygous for both horned and scurred.  In this circumstance, would (could) the scurred gene act as a modifier on the horned gene in some way?  Yeah, I know the question can't be answered in simple terms and I know I'm ignoring alot of other factors trying to find a simple answer.   From my own observations, I tend to think the weak, scurred laterals are more an indication of the hornless gene (if I am going to totally ignore any environmental factors, which I am).  

Linda



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On Fri, 6 May 2005 05:35:23 -0400, Neal and Louise Grose wrote:
> It is impossible for a sheep to be genetically different on one
> part of the head from the other. It may be useful to keep in mind
> that traits that are affected by only one gene are rather rare. For
> example: the size of an animal is affected by thousands of genes
> whose effects are additive. This makes it relatively easy to
> predict the size of an offspring based on the phenotype of the
> parents. This is a trait with high heritability. Blue eyes vs.
> brown eyes in humans are also easy to predict because the trait is
> influenced by one gene (you hazel eyed people don't exist, go away).
>
> So, horns are influenced by different loci on a variety of
> chromosomes: * Horn vs. dominate polled * Horn vs. recessive polled
> (I don't know if the dominate and recessive polled are at the same
> locus)
> * Horn vs. scur, which may share a locus with polled * Sex-linked
> hornless (Shetlands) which must be on the X or Y chromosomes *
> Testosterone production and testosterone receptor genes * A couple
> thousand "size" genes * Physical blood flow impairment to the
> lateral horns due to the dominance of the primary horns   Glad I
> could clear this up for you!   Neal
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